At present, mobile communication systems such as portable telephone systems and radio LANs (Local Area Networks) are widely used. With cellular mobile communication systems, a mobile terminal apparatus is connected to a base station apparatus the coverage area of which includes its present position and can perform radio communication. With cellular mobile communication systems, one possible method for expanding a coverage area or improving communication quality is to install base station apparatuses and base station sending-receiving antennas in many places.
Another possible method for expanding a coverage area or improving communication quality is to use multihop relay communication. For example, a multihop relay communication technique is discussed in the IEEE (Institute of Electrical and Electronics Engineers) 802.16j standard. With the multihop relay communication, a relay station apparatus intervenes between a base station apparatus and a mobile terminal apparatus and can relay radio communication. The mobile terminal apparatus should be connected to any base station apparatus or relay station apparatus. The relay station apparatus may be a fixed radio communication apparatus or a mobile radio communication apparatus.
With the multihop relay communication, the following technique is known. Each mobile station can be connected to other mobile stations. One of mobile stations for which a hop count up to a base station is the lowest is selected as an upper station. By doing so, a multihop relay communication network is built autonomously. In addition, another technique is known. That is to say, after communication is begun, a mobile station at a receiving end informs a mobile station at a sending end about an interference amount in each time slot and the mobile station at the sending end transmits data by the use of a time slot in which an interference amount is small.
Japanese Laid-open Patent Publication No. 2001-237764
Japanese Laid-open Patent Publication No. 2007-194821
With the above method of building a multihop relay communication network, however, many radio communication apparatus each of which functions as a relay station may be set. This may lead to a fall in the efficiency of the operation of an entire mobile communication system. If there are many relay station apparatus, radio frequency interference between relay station apparatus, for example, is problematic. Furthermore, compared with a radio communication apparatus which does not function as a relay station, a radio communication apparatus which functions as a relay station has a disadvantage in power consumption. Accordingly, it is not desirable that excessively many radio communication apparatus function as relay stations.